HOW UNIMAGINABLY strange the world would be if the constants of nature had different values. The so-called fine-structure constant (
), for example, is about 1/137. Were it another value, matter and energy would interact in bizarre ways; indeed, the very distinction between matter and energy could melt away.
Oh, and the blank thing in the bracket is alpha. Some things never change. Physicists call them the constants of nature. Such quantities as the velocity of light,
c, Newton's constant of gravitation,
G, and the mass of the electron,
me, are assumed to be the same at all places and times in the universe.
They form the scaffolding around which the theories of physics are erected, and they define the fabric of our universe.And yet, remarkably, no one has ever successfully predicted or explained any of the constants. Physicists have no idea why they take the special numerical values that they do. In SI units, c is 299,792,458; G is 6.673 X 10-11; and me is 9.10938188 X 10-31--numbers that follow no discernible pattern.
The only thread running through the values is that
if many of them were even slightly different, complex atomic structures such as living beings would not be possible.
No further explanation would then be possible for many of our numerical constants other than that they constitute a rare combination that permits consciousness to evolve.
Our observable universe could be one of many isolated oases surrounded by an infinity of lifeless space--a surreal place where different forces of nature hold sway and particles such as electrons or structures such as carbon atoms and DNA molecules could be impossibilities. If you tried to venture into that outside world, you would cease to be.
Indeed, the word "constant" may be a misnomer. Our constants could vary both in time and in space.
If the extra dimensions of space were to change in size, the "constants" in our three-dimensional world would change with them. And if we looked far enough out in space, we might begin to see regions where the "constants" have settled into different values.
One ratio of particular interest combines the velocity of light,
c, the electric charge on a single electron,
e, Planck's constant,
h, and the so-called vacuum permittivity,
0. This famous quantity,
=
e2/2
0hc, called the fine-structure constant. It quantifies the relativistic (
c) and quantum (
h) qualities of electromagnetic (
e) interactions involving charged particles in empty space (
0). Measured to be equal to 1/137.03599976, or approximately
1/137,
has endowed the number 137 with a legendary status among physicists (it usually opens the combination locks on their briefcases).
Quasars had just been discovered and identified as bright sources of light located at huge distances from Earth. Because the path of light from a quasar to us is so long, it inevitably intersects the gaseous outskirts of young galaxies.
That gas absorbs the quasar light at particular frequencies, imprinting a bar code of narrow lines onto the quasar spectrum.
If the constant was different at the time when the light was absorbed or in the particular region of the universe where it happened,
then the energy required to lift the electron would differ from that required today in laboratory experiments, and the wavelengths of the transitions seen in the spectra would differ. The way in which the wavelengths change depends critically on the orbital configuration of the electrons.
For a given change in , some wavelengths shrink, whereas others increase. The complex pattern of effects is hard to mimic by data calibration errors, which makes the test astonishingly powerful.
When embarking on this project, we anticipated establishing that the value of the fine-structure constant long ago was the same as it is today; our contribution would simply be higher precision.
To our surprise, the first results, in 1999, showed small but statistically significant differences. Further data confirmed this finding.
Based on a total of 128 quasar absorption lines, we found an average increase in of close to six parts in a million over the past six billion to 12 billion years. (SEE THE PICTURE ABOVE)
Further experiment ruled out simple distortion errors with high confidence.
The constants are a tantalizing mystery. Every equation of physics is filled with them, and they seem so prosaic that people tend to forget how unaccountable their values are. Their origin is bound up with some of the grandest questions of modern science, from the unification of physics to the expansion of the universe.
They may be the superficial shadow of a structure larger and more complex than the three-dimensional universe we witness around us.
